By the way, what's the deal with thread pitch? I always worry I'm getting the wrong pitch, but I guess that the whole "standard/fine/extra fine" thread pitch only kicks in with fasteners over 8mm(?). Otherwise, it's a pre-set. Right?

No. It's just the charts that only kick in at 8. They are clearly both a)written by someone who doesn't actually know, themselves, and b)plagarising heavily from each other, and repeating the other's mistakes.

That chart is ****ed up. It says fine but lists more than one thread pitch in the first column, and inconsistently shows extra- and super-fine pitches instead.

The commonly found standard M5 bolt is indeed 0.8 pitch, but the commonly found fine pitch M5 is 0.7. 0.5 must be extra-fine or super-fine. Which is why when you buy a tap and dies set it comes with 5-.8 and 5-.7 but not 5-.5.
I think but am not 100% sure that M6 fine is 0.8 not 0.75.

but I've hardly ever come across them in real life.
No? Are you sure - you've never chased munged up pedal threads? Doing so sends you down to the hardware store for an M10-1.0 tap, because your tap and dies set comes with a 10-1.5 (standard) and 10-1.25 (fine).

There is at least one other place where there is a fine thread, an 8, I think, and I think it's the brake pivot bolt, but am not sure I'm remembering correctly.

What's the thread pitch of derailer hangers?

The "fine thread - course thread" discussion if essentially a very
simplistic categorizing of fasteners. The U.S. Unified thread system
provides a sort of rationalization for a UNC/UNF series but that
didn't and doesn't prevent fasteners being made in a large number of
thread pitches. In U.S. sizes we have, for example, the 1/4"x20tpi
(National Course), the 1/4 x 24 (NS), the 1/4 x 28 (NF), the 1/4 x 32
(NEF) and the 1/4 x 40 (NS).

From memory the difference between American fine and course is the depth of the thread. Course threads cut much deeper into the mating piece to achieve the same amount of metal to metal contact as fine threads.

They are both 60 degree threads but with a flat at the base and peak
and I don't remember whether they are the same. Maybe Frank can check
his Machinery's Handbook (if it is modern enough to include metric
threads :-)

Well, I'm just working from a not very good memory but course threads offer less actual bolt area inside of the threads and hence should not be torqued as high as a fine thread.

On the other hand, fine thread bolts having a shallower thread angle
require less torque to obtain the same clamping force :-)

Fatigue failures typically occur within a couple of threads, where the
bolt engages into the internal thread. Failure is then reached due to
the high stress gradient within the region.

Fatigue failures can be particularly hazardous because they often
occur with no visible warning signs and the failure is often sudden.
Fatigue failures are often unknowingly avoided in gasketed joints
simply because the required crush for the gasket often dictates a
torque or bolt tension that minimizes the risk of a fatigue failure.
However, changing to a new gasket type later on which requires less
crush may be the initial cause of bolt fatigue failure.

It is not unusual to assume that a bolt has failed due to overload
when it has in fact failed from fatigue, which can also be a
consequence of self-loosening.

Also:https://www.excelcalcs.com/engineeri...-joints-fail?/
The first cause listed:
Insufficient Clamp force? - Usually by applying a measured torque load
to the nut bolted joints are tightened to achieve a specific clamp
load. Even under the most extreme applied loads, the clamping force
must prevent joint movement between clamped parts. Movement includes
both opening of the joint to form gaps and slipping. Loads applied to
the joint may be axial forces (in the direction of the bolt axis)
and/or shear forces (perpendicular to the bolt axis). If slippage
occurs then the joint may fail by the bolt loosening. If a gap in the
joint opens then a bolt failure by fatigue is more likely to occur.
Typically bolt fatigue failures occur because of insufficient preload
rather than poor fatigue strength of the bolt. Improving the method of
tightening can reduce the scatter in bolt preload and help guarantee
the minimum required clamping force

You may have worked on machines, including aircraft without fully
understanding what you were doing or why.

You are probably right although the A.F. thought I was competent. Or I
guess that they did as they kept promoting me and they had me managing
divisions for them. Shoot, they even had me writing the skill level
tests for my career field one time.Then when I retired from that job I
hired on as a mechanic again and ended up some years later being
promoted to "Operations Manager" for a fair to middling sized company
in Indonesia.

Get a new stem. This one is a flawed design. There is built-in problem with the shape of the part, and that is a lack of remaining metal around the bolt hole. The stem has been made bigger around the front bolt hole to overcome this, but it still has the 2-bolt-1-failure problem. The traditional shape does not make this concession to ease-of-handlebar-change, and carefully places the single bolt in the rear where there is plenty of metal surrounding the threads.
The traditional design is both less likely to experience a bolt failure, and - in the wild guess dept., be more likely to hold on to the bars and remain usable in the event that one does.

I'm he OP. It so happens that the rear bolt was the one that snapped,
which seems to contradict your assertion about the design's weak point.

Art

And, if I remember correctly, after only 15 years too :-)

This is false logic. There are at least 15 parts on your bike; by your policy we should expect catastrophic part failure once per year.

I'm not quite sure what you are trying to say. A bolt that broke after
15 years of use is somehow associated with something that breaks
annually?

Fatigue failures typically occur within a couple of threads, where the
bolt engages into the internal thread. Failure is then reached due to
the high stress gradient within the region.

Fatigue failures can be particularly hazardous because they often
occur with no visible warning signs and the failure is often sudden.
Fatigue failures are often unknowingly avoided in gasketed joints
simply because the required crush for the gasket often dictates a
torque or bolt tension that minimizes the risk of a fatigue failure.
However, changing to a new gasket type later on which requires less
crush may be the initial cause of bolt fatigue failure.

It is not unusual to assume that a bolt has failed due to overload
when it has in fact failed from fatigue, which can also be a
consequence of self-loosening.

Also:https://www.excelcalcs.com/engineeri...-joints-fail?/
The first cause listed:
Insufficient Clamp force? - Usually by applying a measured torque load
to the nut bolted joints are tightened to achieve a specific clamp
load. Even under the most extreme applied loads, the clamping force
must prevent joint movement between clamped parts. Movement includes
both opening of the joint to form gaps and slipping. Loads applied to
the joint may be axial forces (in the direction of the bolt axis)
and/or shear forces (perpendicular to the bolt axis). If slippage
occurs then the joint may fail by the bolt loosening. If a gap in the
joint opens then a bolt failure by fatigue is more likely to occur.
Typically bolt fatigue failures occur because of insufficient preload
rather than poor fatigue strength of the bolt. Improving the method of
tightening can reduce the scatter in bolt preload and help guarantee
the minimum required clamping force

You may have worked on machines, including aircraft without fully
understanding what you were doing or why.

I have not only worked on cars and agricultural equipment and
industrial equipment (loaders and dozers etc) and been rather
extensively involved with amateur built/homebuilt/experimental
aviation, I have also taught automotive mechanics at the secondary
school AND post secondary (trade) level.

That Figure 10 was not a "failure" per se. The bolt did not break from under tightening - it wore the threads off. Eventually indeed it would have broken.

Head bolts on cars can be said to ALWAYS break from over-torquing. What occurs is that you over-torque the head bolts and then when the engine heats up and expands it blows the top of the bolt off from exceeding the mechanical strength of the bolt. Sometimes you can hear it go.

I rarely use a torque wrench because you can FEEL the torque that should be applied and using a torque wrench a number of times shows you that it almost always feels under-torqued. So you develope a feel for it. A correctly designed piece is supposed to use the mechanical strength of a large number of bolts and not the near maximum strength of a few. This is the mistake that is almost always made on that great "German engineering". They use calculations instead of common sense. Ten headbolts torqued within 10% of the proper torque are better than 6 headbolts designed to carry the load if properly torqued to exactly the correct value.

Which reminds me of what is becoming with the carbon fiber engineering these days. It isn't "great engineering" to make a 12 lb bike that can kill it's rider with a single manufacturing flaw.

A friend, who was an EWO on B-52's, once commented that it wasn't
exactly confidence building to go to war armed with equipment built by
the lowest bidder :-)

By the way, what's the deal with thread pitch? I always worry I'm getting the wrong pitch, but I guess that the whole "standard/fine/extra fine" thread pitch only kicks in with fasteners over 8mm(?). Otherwise, it's a pre-set. Right?

No. It's just the charts that only kick in at 8. They are clearly both a)written by someone who doesn't actually know, themselves, and b)plagarising heavily from each other, and repeating the other's mistakes.

That chart is ****ed up. It says fine but lists more than one thread pitch in the first column, and inconsistently shows extra- and super-fine pitches instead.

The commonly found standard M5 bolt is indeed 0.8 pitch, but the commonly found fine pitch M5 is 0.7. 0.5 must be extra-fine or super-fine. Which is why when you buy a tap and dies set it comes with 5-.8 and 5-.7 but not 5-.5.
I think but am not 100% sure that M6 fine is 0.8 not 0.75.

but I've hardly ever come across them in real life.
No? Are you sure - you've never chased munged up pedal threads? Doing so sends you down to the hardware store for an M10-1.0 tap, because your tap and dies set comes with a 10-1.5 (standard) and 10-1.25 (fine).

There is at least one other place where there is a fine thread, an 8, I think, and I think it's the brake pivot bolt, but am not sure I'm remembering correctly.

What's the thread pitch of derailer hangers?

The "fine thread - course thread" discussion if essentially a very
simplistic categorizing of fasteners. The U.S. Unified thread system
provides a sort of rationalization for a UNC/UNF series but that
didn't and doesn't prevent fasteners being made in a large number of
thread pitches. In U.S. sizes we have, for example, the 1/4"x20tpi
(National Course), the 1/4 x 24 (NS), the 1/4 x 28 (NF), the 1/4 x 32
(NEF) and the 1/4 x 40 (NS).

From memory the difference between American fine and course is the depth of the thread. Course threads cut much deeper into the mating piece to achieve the same amount of metal to metal contact as fine threads.

They are both 60 degree threads but with a flat at the base and peak
and I don't remember whether they are the same. Maybe Frank can check
his Machinery's Handbook (if it is modern enough to include metric
threads :-)

Well, I'm just working from a not very good memory but course threads offer less actual bolt area inside of the threads and hence should not be torqued as high as a fine thread.

On the other hand, fine thread bolts having a shallower thread angle
require less torque to obtain the same clamping force :-)
And it depends what you are threading the bolt into. Using fine
threads in coarse grained cast iron is generally NOT a good idea.

As far as the actual "thread area" there is very little difference. If
you double the TPI the threads are only half as deep, but there are
twice as many threads so the total load bearing area is not much
different.

Fatigue failures typically occur within a couple of threads, where the
bolt engages into the internal thread. Failure is then reached due to
the high stress gradient within the region.

Fatigue failures can be particularly hazardous because they often
occur with no visible warning signs and the failure is often sudden.
Fatigue failures are often unknowingly avoided in gasketed joints
simply because the required crush for the gasket often dictates a
torque or bolt tension that minimizes the risk of a fatigue failure.
However, changing to a new gasket type later on which requires less
crush may be the initial cause of bolt fatigue failure.

It is not unusual to assume that a bolt has failed due to overload
when it has in fact failed from fatigue, which can also be a
consequence of self-loosening.

Also:https://www.excelcalcs.com/engineeri...-joints-fail?/
The first cause listed:
Insufficient Clamp force? - Usually by applying a measured torque load
to the nut bolted joints are tightened to achieve a specific clamp
load. Even under the most extreme applied loads, the clamping force
must prevent joint movement between clamped parts. Movement includes
both opening of the joint to form gaps and slipping. Loads applied to
the joint may be axial forces (in the direction of the bolt axis)
and/or shear forces (perpendicular to the bolt axis). If slippage
occurs then the joint may fail by the bolt loosening. If a gap in the
joint opens then a bolt failure by fatigue is more likely to occur.
Typically bolt fatigue failures occur because of insufficient preload
rather than poor fatigue strength of the bolt. Improving the method of
tightening can reduce the scatter in bolt preload and help guarantee
the minimum required clamping force

You may have worked on machines, including aircraft without fully
understanding what you were doing or why.

You are probably right although the A.F. thought I was competent. Or I
guess that they did as they kept promoting me and they had me managing
divisions for them. Shoot, they even had me writing the skill level
tests for my career field one time.Then when I retired from that job I
hired on as a mechanic again and ended up some years later being
promoted to "Operations Manager" for a fair to middling sized company
in Indonesia.

Peter principal at work? It was all "Government work"

You are trying to spell "sour grapes" perchance?
Not a chance!!!! I've worked for enough idiots without having to work
for for politicians and bureaucrats.
Teaching in the public school system was enough politics for me.

Sure, you get a fat pension which I'll have to do without - and I
could have if I'd stayed teaching.

Fatigue failures typically occur within a couple of threads, where the
bolt engages into the internal thread. Failure is then reached due to
the high stress gradient within the region.

Fatigue failures can be particularly hazardous because they often
occur with no visible warning signs and the failure is often sudden.
Fatigue failures are often unknowingly avoided in gasketed joints
simply because the required crush for the gasket often dictates a
torque or bolt tension that minimizes the risk of a fatigue failure.
However, changing to a new gasket type later on which requires less
crush may be the initial cause of bolt fatigue failure.

It is not unusual to assume that a bolt has failed due to overload
when it has in fact failed from fatigue, which can also be a
consequence of self-loosening.

Also:https://www.excelcalcs.com/engineeri...-joints-fail?/
The first cause listed:
Insufficient Clamp force? - Usually by applying a measured torque load
to the nut bolted joints are tightened to achieve a specific clamp
load. Even under the most extreme applied loads, the clamping force
must prevent joint movement between clamped parts. Movement includes
both opening of the joint to form gaps and slipping. Loads applied to
the joint may be axial forces (in the direction of the bolt axis)
and/or shear forces (perpendicular to the bolt axis). If slippage
occurs then the joint may fail by the bolt loosening. If a gap in the
joint opens then a bolt failure by fatigue is more likely to occur.
Typically bolt fatigue failures occur because of insufficient preload
rather than poor fatigue strength of the bolt. Improving the method of
tightening can reduce the scatter in bolt preload and help guarantee
the minimum required clamping force

You may have worked on machines, including aircraft without fully
understanding what you were doing or why.

I have not only worked on cars and agricultural equipment and
industrial equipment (loaders and dozers etc) and been rather
extensively involved with amateur built/homebuilt/experimental
aviation, I have also taught automotive mechanics at the secondary
school AND post secondary (trade) level.

That Figure 10 was not a "failure" per se. The bolt did not break from under tightening - it wore the threads off. Eventually indeed it would have broken.

Head bolts on cars can be said to ALWAYS break from over-torquing. What occurs is that you over-torque the head bolts and then when the engine heats up and expands it blows the top of the bolt off from exceeding the mechanical strength of the bolt. Sometimes you can hear it go.

I rarely use a torque wrench because you can FEEL the torque that should be applied and using a torque wrench a number of times shows you that it almost always feels under-torqued. So you develope a feel for it. A correctly designed piece is supposed to use the mechanical strength of a large number of bolts and not the near maximum strength of a few. This is the mistake that is almost always made on that great "German engineering". They use calculations instead of common sense. Ten headbolts torqued within 10% of the proper torque are better than 6 headbolts designed to carry the load if properly torqued to exactly the correct value.

Which reminds me of what is becoming with the carbon fiber engineering these days. It isn't "great engineering" to make a 12 lb bike that can kill it's rider with a single manufacturing flaw.

A friend, who was an EWO on B-52's, once commented that it wasn't
exactly confidence building to go to war armed with equipment built by
the lowest bidder :-)
"a loose gaggle of compromises flying in close formation" - which is
why I'm building my own - - -

Fatigue failures typically occur within a couple of threads, where the
bolt engages into the internal thread. Failure is then reached due to
the high stress gradient within the region.

Fatigue failures can be particularly hazardous because they often
occur with no visible warning signs and the failure is often sudden.
Fatigue failures are often unknowingly avoided in gasketed joints
simply because the required crush for the gasket often dictates a
torque or bolt tension that minimizes the risk of a fatigue failure.
However, changing to a new gasket type later on which requires less
crush may be the initial cause of bolt fatigue failure.

It is not unusual to assume that a bolt has failed due to overload
when it has in fact failed from fatigue, which can also be a
consequence of self-loosening.

Also:https://www.excelcalcs.com/engineeri...-joints-fail?/
The first cause listed:
Insufficient Clamp force? - Usually by applying a measured torque load
to the nut bolted joints are tightened to achieve a specific clamp
load. Even under the most extreme applied loads, the clamping force
must prevent joint movement between clamped parts. Movement includes
both opening of the joint to form gaps and slipping. Loads applied to
the joint may be axial forces (in the direction of the bolt axis)
and/or shear forces (perpendicular to the bolt axis). If slippage
occurs then the joint may fail by the bolt loosening. If a gap in the
joint opens then a bolt failure by fatigue is more likely to occur.
Typically bolt fatigue failures occur because of insufficient preload
rather than poor fatigue strength of the bolt. Improving the method of
tightening can reduce the scatter in bolt preload and help guarantee
the minimum required clamping force

You may have worked on machines, including aircraft without fully
understanding what you were doing or why.

You are probably right although the A.F. thought I was competent. Or I
guess that they did as they kept promoting me and they had me managing
divisions for them. Shoot, they even had me writing the skill level
tests for my career field one time.Then when I retired from that job I
hired on as a mechanic again and ended up some years later being
promoted to "Operations Manager" for a fair to middling sized company
in Indonesia.

Peter principal at work? It was all "Government work"

You are trying to spell "sour grapes" perchance?
Not a chance!!!! I've worked for enough idiots without having to work
for for politicians and bureaucrats.

But one isn't working for a politician when in the service. At least
not when assigned to units that actually have a mission. For example,
I was assigned to one of the two reconnaissance squadrons in the A.F.
equipped with a super long focal length camera. One in Asia and one in
Europe. When you fly missions designated by headquarters USAF they
aren't politicians directing you. I was assigned to the "Gun Ship
Squadron" (puff the magic dragon) where we bragged that if we got
there before they actually got inside the wire we never lost a post.
Not too many politicians there either. Then, lets see, I was assigned
to one of the wings that was flying the SAC airborne nuclear flights,
very serious folks those nuclear chaps, and, oh yes, we provided
support for the U-2 flights over Cuba that told y'all that the
missiles weren't there.

Not many politicians in the operational military (as opposed to the
training units).

Teaching in the public school system was enough politics for me.

Sure, you get a fat pension which I'll have to do without - and I
could have if I'd stayed teaching.

Nope, it is rather a thin pension compared to my active duty pay. You
see, what with longevity pay, overseas pay, flight pay, quarters and
rations, etc., active service personnel may draw nearly double their
base salary. When retirement arrives you receive (for 20 years) only
1/2 of your base salary.

By the way, what's the deal with thread pitch? I always worry I'm getting the wrong pitch, but I guess that the whole "standard/fine/extra fine" thread pitch only kicks in with fasteners over 8mm(?). Otherwise, it's a pre-set. Right?

No. It's just the charts that only kick in at 8. They are clearly both a)written by someone who doesn't actually know, themselves, and b)plagarising heavily from each other, and repeating the other's mistakes.

That chart is ****ed up. It says fine but lists more than one thread pitch in the first column, and inconsistently shows extra- and super-fine pitches instead.

The commonly found standard M5 bolt is indeed 0.8 pitch, but the commonly found fine pitch M5 is 0.7. 0.5 must be extra-fine or super-fine. Which is why when you buy a tap and dies set it comes with 5-.8 and 5-.7 but not 5-.5.
I think but am not 100% sure that M6 fine is 0.8 not 0.75.

but I've hardly ever come across them in real life.
No? Are you sure - you've never chased munged up pedal threads? Doing so sends you down to the hardware store for an M10-1.0 tap, because your tap and dies set comes with a 10-1.5 (standard) and 10-1.25 (fine).

There is at least one other place where there is a fine thread, an 8, I think, and I think it's the brake pivot bolt, but am not sure I'm remembering correctly.

What's the thread pitch of derailer hangers?

The "fine thread - course thread" discussion if essentially a very
simplistic categorizing of fasteners. The U.S. Unified thread system
provides a sort of rationalization for a UNC/UNF series but that
didn't and doesn't prevent fasteners being made in a large number of
thread pitches. In U.S. sizes we have, for example, the 1/4"x20tpi
(National Course), the 1/4 x 24 (NS), the 1/4 x 28 (NF), the 1/4 x 32
(NEF) and the 1/4 x 40 (NS).

From memory the difference between American fine and course is the depth of the thread. Course threads cut much deeper into the mating piece to achieve the same amount of metal to metal contact as fine threads.

They are both 60 degree threads but with a flat at the base and peak
and I don't remember whether they are the same. Maybe Frank can check
his Machinery's Handbook (if it is modern enough to include metric
threads :-)

Well, I'm just working from a not very good memory but course threads offer less actual bolt area inside of the threads and hence should not be torqued as high as a fine thread.

On the other hand, fine thread bolts having a shallower thread angle
require less torque to obtain the same clamping force :-)
And it depends what you are threading the bolt into. Using fine
threads in coarse grained cast iron is generally NOT a good idea.

As far as the actual "thread area" there is very little difference. If
you double the TPI the threads are only half as deep, but there are
twice as many threads so the total load bearing area is not much
different.

You missed the point. Because fine threads are at a shallower angle
then coarse threads the clamping (linear) force is greater for the
same torque.